Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q9.5
[15 points.] In cluster 1, the main sequence extends from spectral class O to spectral class K. In cluster 2, there are no main sequence stars cooler than spectral class F. Determine which star cluster is older, and explain the reasoning behind your choice.
Solution and grading rubric:
- p = 15/15:
Correct. The OBAFGKM main sequence runs from massive to medium to low-mass. Massive stars become main sequence stars sooner, and spend less time as main sequence stars than medium mass stars. Since cluster 1 (OBAFGK) has more medium-mass stars on the main sequence than cluster 2 (OBAF), then cluster 1 must be older, as more time was required for its spectral class G and K stars to reach its main sequence. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Recognizes the relationship between mass (inferred from spectral type -> temperature -> luminosity -> mass along the main sequence line), and main sequence lifetime, but rest of discussion is garbled or incomplete. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least mentions some understanding of the relationships between mass and evolution times. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 4160
p: 5 students
r: 9 students
t: 10 students
v: 14 students
x: 1 student
y: 1 student
z: 0 students
A sample "p" response (from student 1223):
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